The invention relates to a fan for a cooling system of a motor vehicle, having a radial impeller with several vanes disposed between an impeller bottom and a cover disk, wherein a stationary intake nozzle extends axially into a cover disk intake provided with a radius of curvature, and forms an annular gap between the cover disk intake and the intake nozzle.
A fan for a cooling system of a motor vehicle is known from German Patent Publication DE 25 30 742 C3, which has a radial impeller disposed, viewed in the direction of air flow, in back of a heat exchanger of a coolant circuit of the cooling system. The radial impeller is driven via a fluid friction clutch. The fan is used to generate an appropriate air flow through the heat exchanger, in particular when the motor vehicle is stopped or moves slowly and there is insufficient air flow from movement.
Due to the large number of fans to be used in passenger cars, they are as a rule made in one piece by injection molding as described in Bosch, "Kraftfahrtechnisches Taschenbuch" [Automotive Handbook], vol. 21, published by VDI Verlag, Dusseldorf, 1991, page 413.
It is an object of the invention to provide a fan of the above-mentioned type which is suitable for being produced in large numbers and is designed to have advantageous flow properties.
These and other objects have been attained according to preferred embodiments of the invention by providing a fan for a cooling system of a motor vehicle, having a radial impeller with a plurality of vanes disposed between an impeller bottom and a cover disk, and having a stationary intake nozzle extending axially into a cover disk intake, forming an annular gap between the cover disk intake and the intake nozzle, wherein the impeller bottom, the vanes and the cover disk of the radial impeller are made in one piece of a plastic material, and wherein a separate air guide ring is arranged on the cover disk proximate the cover disk intake.
Due to the one-piece production of the radial impeller from a plastic material it is possible to produce a large number of pieces economically. To be able to unmold the impeller from an appropriate plastic injection molding tool, no undercuts which would prevent unmolding should be provided. Furthermore, sucker pins of the injection molding tool, by means of which the vanes of the radial impeller are defined, must have rugged and wear-resistant structural shapes in order to allow a dependable and clean production of the vanes. To prevent the gap between the cover disk intake and the intake nozzle from becoming too large because of the requirements of plastics technology, which would lead to loss of efficiency and increased noise generation, the separate air guide ring has been seated aligned against the cover disk in the area of the cover disk intake.
By using a separate air guide ring for the area of the cover disk intake, is possible to produce the radial impeller in accordance with improved technical flow aspects, while at the same time meeting the requirement of its unmolding as a plastic part, since the area which is critical for the production in accordance with plastics technology, namely the cover disk intake, is formed by separate component. Accordindgly, it is possible to achieve a gap between the cover disk and the intake nozzle which is narrower and is optimized from the viewpoint of flow technology. This results in an improvement of the degree of efficiency and in a reduced noise generation when the fan is operated. In this case the invention relates to all types of radial impellers, whether they have vanes which are backwardly inclined opposite to the direction of rotation, or curved, or radially disposed and/or curved in the direction of rotation.
In accordance with one embodiment of the invention, an inside of the air guide ring is provided with a radius of curvature adapted to the cover disk intake. The radius of curvature of the inside of the air guide ring is preferably either identical to or approximately identical to the radius of curvature of the cover disk intake. By means of this arrangement, an inflow radius is provided in the area of the cover disk intake which is advantageous in accordance with flow technology and which conveys the flow guided back through the gap as well as the main flow into the impeller without separation.
In a further embodiment of the invention, the cover disk as well as the air guide ring) are rounded in the area of their transition on the flow side. This is advantageous if the air guide ring is disposed eccentrically to some degree in respect to the cover disk. Because of this rounding, the separation of the flow passing through the gap is prevented at the connection between the air guide ring and the cover disk on the flow side, by means of which eddy effects which reduce the degree of efficiency of the radial impeller are prevented.
In a preferred embodiment of the invention, the vanes are backwardly inclined or curved in relation to the direction of rotation of the radial impeller. In a further embodiment of the invention a number of vane extensions, which are aligned with the corresponding, associated vanes, are provided on the air guide ring in the extension of each vane leading edge of the radial impeller. In this way, the vane leading edge is elongated, opposite to the flow direction, forward toward the cover disk intake, preventing a detrimental impact of the gap air on the front edges of the backwardly inclined or curved vanes.
In accordance with a further embodiment of the invention a circumferential support collar is provided on the air guide ring, which can be fastened on a corresponding fastening collar of the cover disk with the aid of connecting means. A stable fastening of the air guide ring on the cover disk is provided by this arrangement, which additionally achieves a mutual support effect.
In a further embodiment of the invention the air guide ring is made of a plastic material. In this way, it is possible to design the ring relatively thin so that it has only little weight. For this reason the ring can cause only slight unbalancing when eccentrically placed.
In a further embodiment of the invention the air guide ring is made of a material with a higher density and rigidity than a plastic material. Magnesium is particularly suited for this embodiment. Consequently, the air guide ring has a relatively high sturdiness and assumes a support function by which the impeller sturdiness is increased.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.